Probable Cause #25: Controlling The Approach

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This article originally appeared in IFR Refresher, Dec. 2005.

Probable Cause

What do you do when the controller who is vectoring you to the final approach fails to put you in the proper position?

In the summer of 2004, a pilot flying a Piper Cherokee Six from Springfield, Ky., to Hot Springs/Memorial Field (KHOT) in Hot Springs, Ark., was put into such a situation. Unfortunately, the pilot's attempt to salvage the approach instead of going missed resulted in tragedy.

The flight was conducted under IFR even though the weather at the destination was VMC. The cloud cover was thin, but there were several layers that the aircraft had to descend through to reach the airport at Hot Springs.

The aircraft had departed Springfield at approximately 7 a.m. on the day of the accident. The flight proceeded normally and three hours later, while cruising at 5000 feet, the pilot checked in with Memphis Center. The controller acknowledged the transmission and instructed the pilot to fly a 200-degree heading as he began to vector him for the ILS 5 approach at KHOT. After another heading change and an ATC-requested speed reduction of 15 kts, the controller instructed the pilot to descend and maintain 4000 feet. The controller also told the pilot to fly a heading of 010 degrees to intercept the localizer, adding that, "I'm going to bring you in a little bit high, if that's OK?" The pilot said that it was fine with him.

In the next transmission, the controller undoubtedly intended to clear the pilot for his approach to Hot Springs. "N4123R, your position is eight miles southeast of HOSSY (the locater outer marker), fly heading 020, intercept the localizer, maintain 3000 until established." The pilot acknowledged the transmission and added that he would let the controller know when he was established. He did not ask if he was cleared for the approach, nor did the controller realize that he hadn't properly cleared the pilot to do so.

Shortly thereafter, another controller relieved the controller handling 23R. A relief briefing was conducted and there was a short discussion regarding the aircraft's approach. The handling controller told the relief controller, "He's probably going to miss. I turned him on too late, probably going to miss. Yeah, he's too high. He missed it now. He missed it. He's too high."

Just then, the pilot called to say that he was established. The relief controller responded with, "Change to advisory approved. Report your arrival time this frequency." The pilot responded by saying, "23R, cleared for the ILS runway five. I'll report to you when I am down." No further transmissions were received from the aircraft.

Never Established

Piper PA-32 Cherokee Six

A radar plot prepared by the FAA of the aircraft's track indicates that the aircraft flew back and forth across the localizer several times while the pilot was communicating with ATC. When the communications ended, the track settled down with the aircraft slightly right of the centerline of the localizer. The aircraft flew directly over the runway and the center of the airport at approximately 2500 feet, about 2000 feet above the surface. The decision height for the approach is 715 feet, 200 feet above the surface. The last radar plot showed the airplane flying straight ahead at 2000 feet with the airport behind him. The aircraft would eventually strike the south side of Indian Mountain, located inside the Hot Springs National Park, at the 950-foot level, killing the pilot who was the sole occupant on board.

The pilot had a handheld GPS with him in the aircraft and it was operating during the approach. Investigators downloaded the aircraft's track from the unit, which revealed that the aircraft crossed abeam HOSSY at 3055 feet MSL at a groundspeed of 127 knots. The track also shows a series of right and left turns across the localizer.

The aircraft crossed abeam the missed approach point at 2536 feet, approximately 1800 feet above the glide slope at 114 knots. The airplane continued to descend as it flew away from the airport on a northeasterly heading. The last 11 seconds of data shows that the aircraft began a left turn to the north before the data ended at 10:43 a.m. at an altitude of 970 feet, and a ground speed of 111 knots. The last GPS coordinate was approximately five miles northeast of the airport.

At 10:35 a.m., the Hot Springs ASOS reported the weather as winds from 220 degrees at eight kts with a visibility of 8 SM. There was an overcast layer at 7000 feet, a broken layer at 4200 feet and scattered clouds at 1200 feet.

Since the airplane passed over the airport at about 2500 feet, it would have been above the lowest cloud layer at 1200 feet. The ASOS reported that layer as scattered, but it may not have been. Had it been scattered the pilot should have seen the airport as he approached it. But based on how the approach was flown, it's reasonable to assume that the pilot's positional awareness was not what it should have been. He may have been concentrating on the instruments and trying to get the airplane down rather than looking out the window at that point.

The winds aloft were not reported in the accident report, but with a southwest wind at eight kts on the surface it is entirely possible that the tail wind at 2000 feet was much stronger and pushing the airplane along faster than the pilot expected.

Positional Awareness

Hot Springs (KHOT) ILS Rwy 5 Approach (excerpt). Click here for full-size version.

The pilot held a private pilot certificate with single-engine land and instrument ratings. He possessed a current medical and he had accumulated approximately 1,750 hours in flight, of which 115 hours were simulated instrument flight and 58 hours of actual instrument time. His flight review was current.

The terrain where the wreckage came to rest is heavily wooded and the upslope is approximately 60 degrees. Investigators found no pre-existing anomalies that could have explained why the aircraft crashed.

The pilot may have been lulled into a false sense of security when the controller told him he was going to vector him in "just a bit high." But what is just a bit high?

The aircraft should have crossed HOSSY at 2,213 feet on the glide slope. The GPS indicates that it crossed HOSSY at 3,055 feet, 842 feet high. It would seem that it was more than "just a bit high." Also, the aircraft should have intercepted the glide slope at 2,500 feet outside of HOSSY. Since it was so high it never had any chance of a normal ILS approach.

Also, if a controller observes an aircraft deviate from the final approach course after the initial intercept he is required to inform the pilot of his position and ask his intentions. This was not done.

But what is the pilot's responsibility for knowing his own position? Positional awareness is exceedingly important at all times during instrument flight. Had the pilot realized his position relative to the airport, this accident would not have happened.

He did have his handheld GPS in the aircraft and it was operating. A glance at it would have revealed the location of the airport at any time during the faulty approach sequence.

The controller told him he was high, but it doesn't appear that the pilot did anything about it. He didn't seem to descend at a rate high enough to capture the glide slope, so he probably felt that he was still several miles from the airport when in fact he was right over it.

The glide slope needle should have been another indicator. Even if he did not pay attention to his handheld GPS, the fact that the glide slope needle never left the bottom of the gauge should have alerted him to the fact that he needed to rethink what he was doing.

Both controllers knew that the aircraft was too high to make a successful approach, as evident by the remarks made by the handling controller that he expected the pilot to miss the approach. Why didn't either of them say anything, as is required by the Air Traffic Control Handbook?

They both may have been distracted by the controller changeover. That should not be seen as an excuse because relief briefings are designed to prevent just such a thing from occurring. But if the controller being relieved was in a hurry to leave the position, for whatever reason, that may have presented just the distraction that prevented him from warning the pilot about his location.

The relieving controller may have believed that the pilot was missing the approach because of his altitude. But the missed approach procedure is a climb to 1100 feet followed by a climbing right turn to 3000 feet. He did not see that occur because the airplane continued straight ahead for about five miles. Yet, the relieving controller told the pilot to switch frequencies rather than warn him about his position.

The Cherokee Six pilot thought the weather was better than it may have been. With eight miles visibility he may have thought that he could meander down, break out of the clouds, and see the runway in time to make a safe landing. But that was not the case. AWOS and ASOS reports are not always accurate and they only report what is directly over the location of the system's sensors. Perhaps it saw the clouds as scattered at that location when they were really broken or overcast around the airport. A layer at 1200 feet AGL is approximately 1740 feet MSL at Hot Springs. The airplane did not descend below that until it was well beyond the airport, in the vicinity of Indian Mountain where the weather was probably not as good.

Lessons To Learn

Handheld GPS

What kind of lesson can you learn from this accident? For one thing, it demonstrates how important positional awareness is to the pilot who is operating close to the ground in IMC. You cannot afford to let your guard down and not know where you are at all times in relation to the airport you are approaching.

With the GPS revolution there is no reason for a pilot not to know exactly where he is at all times. Most have moving map displays that show the aircraft's position relative to the waypoint that is current. The accident report did not detail what type of GPS the pilot had in the aircraft or whether it had a moving map display. But certainly it held information that could have avoided the accident had the pilot paid attention to it.

The NTSB split the blame for the accident between the pilot, for his failure to fly a stabilized approach, and ATC, for its failure to provide known information that may have assisted the pilot in determining whether to continue with the approach or take alternate action.

Reading the accident report, it is apparent that had the pilot or the two controllers who were involved paid more attention to what was going on around them that this accident could have been prevented. It should also tell each of you that you cannot completely rely on controllers. While they are consummate professionals, they are human and make mistakes. It is up to the pilot to maintain his own positional and situational awareness so that should a controller make a mistake, the pilot will catch it before it turns into an accident.


More accident analyses are available in AVweb's Probable Cause Index. And for monthly articles about IFR flying including accident reports like this one, subscribe to AVweb's sister publication, IFR Refresher.